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Port 4851 (derby-repli)

IANA assigns port 4851 to derby-repli: Apache Derby Replication.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
derby-repli TCP Apache Derby Replication Jorgen Loland -
derby-repli UDP Apache Derby Replication Jorgen Loland -

Registry dates for this port: registered 2008-02-27.

Check what is listening on port 4851

Linux: is anything listening on TCP 4851?
sudo ss -tlnp 'sport = :4851'
Linux: UDP 4851
sudo ss -ulnp 'sport = :4851'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4851
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4851 '
Windows (Command Prompt)
netstat -ano | findstr :4851
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4851 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4851
From Windows
Test-NetConnection HOST -Port 4851
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4851

Block port 4851 in the firewall

ufw
sudo ufw deny 4851/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4851 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4851 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4851' -Direction Inbound -Protocol TCP -LocalPort 4851 -Action Block
ufw
sudo ufw deny 4851/udp
iptables
sudo iptables -A INPUT -p udp --dport 4851 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4851 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4851' -Direction Inbound -Protocol UDP -LocalPort 4851 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.